In the related art, a paper sheet processing apparatus is known which sorts paper sheets such as bills based on a type or a damage level thereof.
When a paper sheet is torn and a reinforcing material such as a tape is pasted on the paper sheet, the thickness of the paper sheet in the part on which the reinforcing material is pasted is different from the thickness on the other parts. Accordingly, the paper sheet processing apparatus detects a damage level of a paper sheet by detecting the thickness of the paper sheet.
A thickness detecting device is known as a device that detects a thickness of a paper sheet.
The thickness detecting device presses a conductive measuring target of metal or the like on a paper sheet and detects the thickness of the paper sheet based on a distance to the measuring target which varies depending on the thickness of the paper sheet.
The thickness detecting device includes, for example, a noncontact displacement sensor having a coil and an oscillation circuit. The thickness detecting device detects the distance between the coil and the measuring target by detecting a variation in oscillation frequency or inductance of the oscillation circuit which varies depending on the distance between the coil and the measuring target.
In the thickness detecting device according to the related art, when a plurality of planar coil patterns are arranged closely on a planar board to detect a thickness of the entire surface of a paper sheet, the oscillation circuits may interfere with each other due to a pull-in phenomenon or a coupling phenomenon and thus may not detect the thickness of the paper sheet with high accuracy.